As it is well known, an operation of discharge lamps is based on a voltaic arc determined by the discharge between two electrodes. It is also known that it is not possible to obtain in this type of lamps an adjustment of intensity in the range between 0% and 100%, which is possible with filament lamps, since it would cause the switching off of the arc and in any case a very unstable operation at the intermediate power values.
At present, to obtain the adjustment of the light intensity of the discharge lamp, a mechanical shutter is mounted in front of the projector, making it possible to vary the light intensity, blocking the light rays emitted from the projector.
This kind of solution, even though it has been used for many years, is characterized by some drawbacks, among which possible to mention is a remarkable increase of weight, sizes and unbalancing of the weight with respect to the fulcrum of the projector, as well as a remarkable increase of total costs.
Mainly, said solution induces geometric aberrations of the emitted light beam, reducing the light efficiency of the projector when the shutter is fully open.